1. Field of the Invention
The present invention relates to an optical collimator comprising an optical fiber array for aligning and fixing optical fibers, and a microlens array arranged near the optical fiber array at a predetermined distance and a method of aligning optical axes of the optical collimator.
2. Description of the Related Art
Recently, an array of Exiton Absorption Reflection Switch (EARS) having a signal regeneration function is paid attention to in, for example, TECHNICAL REPORT OF IEICE A-P92-78, SSE92-70 (1992-10) "Experiment digital free-space photonic switch". In this EARS, an optical collimator array is used at a light incident portion and a light exit portion thereof. This optical collimator array functions to supply light signals emitted through optical fibers into a two-dimensional photonic device as parallel light.
The optical collimator array comprises an optical fiber array for aligning and fixing optical fibers, and a microlens array arranged near the optical fiber array at a predetermined distance. In the optical collimator mentioned above, one end portion of the optical fiber array is faced to one end of the microlens array at a distance substantially equal to a focal length of the microlens array. Therefore, diverging light emitted from the optical fiber array is converted into parallel light.
As to a manufacturing method of the optical collimator array mentioned above, it is assumed that the optical fiber array and the microlens array are arranged on the same substrate and are spaced at a distance substantially equal to a focal length. However, in the manufacturing method mentioned above, it is very difficult to arrange the optical fiber array and the microlens array with a distance substantially equal to a focal length and to make coincident axes of the optical fibers of the optical fiber array with axes of the microlens array. Moreover, in the construction mentioned above, a strength of the optical collimator array is lowered and a handling of the optical collimator array becomes difficult.
That is to say, in order to align the light axes in the optical collimator array having the construction mentioned above, light is made incident upon one end of the optical fiber array being opposite to an end facing to the microlens array, and then light emitted from the microlens array is picked up by for example CCD camera and is displayed on a monitor. Then, spots of the light displayed on the monitor are aligned in one direction by moving the optical fiber array and the microlens array relatively. After the spots are aligned in the manner mentioned above, the optical fiber array and the microlens array are connected by using for example adhesives of ultraviolet hardening type.
In the method mentioned above, if a positional relation between the optical fiber array and the microlens array is varied, the spots on the monitor (4 optical fibers in the optical fiber array) are not aligned in one direction as shown in FIG. 15(a), and thus it is understood that the optical fiber array and the microlens array are not arranged properly. However, if the optical fiber array and the microlens array are varied in a thickness direction i.e., parallel, the spots on the monitor are aligned in one direction i.e., on the line, and thus it is not understood that the optical fiber array and the microlens array are not arranged properly. Therefore, in the latter case, it is not possible to make completely coincident the light axes of the optical fibers in the optical fiber array with the light axes of the microlens in the microlens array.